The present invention relates to a method for forming a copper wiring in a semiconductor device, and more particularly, to a method for forming a copper wiring in a semiconductor device that can prevent copper (Cu) ions from migrating over time after conducting a CMP (chemical mechanical polishing) process for a copper layer.
As the design rule of a semiconductor device decreases, circuits are being designed using a multi-layered wiring structure. In this regard, as the design rule of a semiconductor device decreases below 130 nm and the feature size of a transistor is reduced, the operation of the semiconductor device should improve in conformity with the decrease in the design rule. However, as the gap between metal wirings of the semiconductor device decreases, the parasitic capacitance induced between the metal wirings increases. As a result, the operation of the semiconductor device tends to deteriorate.
In order to cope with this problem, copper (Cu) has recently been used as the material for the metal wirings of the semiconductor device in place of aluminum (Al). Since copper has excellent electrical conductivity and a low resistance when compared to aluminum and tungsten, it is possible to solve the problems associated with RC signal delay in a semiconductor device having a high level of integration and a high operation speed.
However, it is not easy to etch copper. Therefore in order to form a copper wiring, a damascene process is employed. The damascene process is divided into a single damascene process and a dual damascene process. In the case of a dual damascene process, it is possible to simultaneously form a copper wiring and a contact plug for rendering electrical connection with an underlying layer. As a result, a dual damascene process is advantageous in terms of processing as compared to a single damascene process.
In a metal wiring formed of copper, EM (electromigration) characteristics, SM (stress migration) characteristics, and TDDB (time dependent dielectric breakdown) characteristics are important aspects. In particular, in the case of the TDDB characteristics, when using existing metals such as aluminum and tungsten as the material of wirings, serious problems are avoided. However, when copper is used, the TDDB characteristics are important since the diffusion of copper ions actively occurs. For example, after a CMP process is conducted for a copper layer, the migration of copper ions over time is an important factor that causes a bridge phenomenon between adjoining copper wirings, the deterioration of leakage current characteristics, and the occurrence of a TDDB failure.